Fast all-optical switching of information is an essential element of modem optical communication systems, enabling the slower electronic functions to be reserved only for the input and output terminals of the network, where the speeds required are those of individual channels, and not of the network throughput. In WDM systems, the information is segregated with regard to its source and destination according to the wavelength of the particular optical signal being transferred, and a switch for use in such a system must therefore be able to route each signal automatically according to its wavelength.
There exist a number of prior art devices for performing this function, such as that described in U.S. Pat. No. 5,414,540 to J. S. Patel et al., for “Frequency-selective optical switch employing a frequency dispersive element, polarization dispersive element and polarization modulating elements”, hereby incorporated by reference in its entirety, and those devices mentioned in the references cited therein. However, most of those devices have one or more disadvantages in that they are either complicated to build, or to align, or utilize expensive component parts. For instance, the complete embodiment of the switch described in U.S. Pat. No. 5,414,540 contains on its input side, as illustrated in FIG. 11 of the patent, a wavelength dispersive element (not shown), a polarization dispersive element to displace the beam polarizations, such as a birefringent crystal, a half-wave plate element, a focusing element, another polarization dispersive element such as another birefringent crystal, and a segmented liquid crystal polarization modulator. The same number of components are required on the output side also. In the embodiment shown in FIGS. 1-4, the input elements include a polarization alignment component (not shown) to provide a specific polarization direction to the input beam, a wavelength dispersive element, a focussing element, a polarization displacement element such as a birefringent crystal, and a segmented liquid crystal polarization modulator. In addition, the same components are required on the output side also. Such a switch, in any of its embodiments, therefore contains a large number of components and is thus complicated to construct.
There therefore exists a need for a simple wavelength-selective optical switch, employing a smaller number of separate components than that of commonly available current devices.
The disclosures of each of the publications mentioned in this section and in other sections of the specification, are hereby incorporated by reference, each in its entirety.